Index is used incorrectly if constant part of the string ends with \d,
probably also with other escapes.
foo=# explain select count(*) from loc where url ~ '^http://www\\.7-eleven\\.com/newsroom/articles\\.asp\\?p=\\d+';
QUERYPLAN
Aggregate (cost=3.46..3.46 rows=1 width=0) -> Index Scan using url_index on loc (cost=0.00..3.46 rows=1 width=0)
Index Cond: ((url >= 'http://www.7-eleven.com/newsroom/articles.asp?p=d'::text) AND (url <
'http://www.7-eleven.com/newsroom/articles.asp?p=e'::text)) Filter: (url ~
'^http://www\\.7-eleven\\.com/newsroom/articles\\.asp\\?p=\\d+'::text) (4 rows)
foo=# select count(*) from loc where url ~ '^http://www\\.7-eleven\\.com/newsroom/articles\\.asp\\?p=\\d+';count-------
0
(1 row)
foo=# set enable_indexscan = off;
SET
foo=# explain select count(*) from loc where url ~ '^http://www\\.7-eleven\\.com/newsroom/articles\\.asp\\?p=\\d+';
QUERY PLANAggregate (cost=3056.41..3056.41 rows=1 width=0) -> Seq Scan on loc
(cost=0.00..3056.40rows=1 width=0) Filter: (url ~
'^http://www\\.7-eleven\\.com/newsroom/articles\\.asp\\?p=\\d+'::text) (3 rows)
foo=# select count(*) from loc where url ~'^http://www\\.7-eleven\\.com/newsroom/articles\\.asp\\?p=\\d+';count-------
281
(1 row)
--
Antti Salmela
